We take public companies owning investment links and undertaking the same accounting firm, which is called "shared auditor" from 2007 to 2015 as example to explore the information sharing effect and low-balling effect in the special phenomenon "shared auditor" in the stock-holding relationship by comparing the audit quality and audit fees in both the investors and investees. We finally find that the information sharing effect is more significant when the two in the investment link share the same accounting firm. We find when two companies share audit, their audit quality and audit fees of investors will grow up obviously. In additional research, we find both the investors and investees will find the most cost-effective and beneficial way to get information and maximize the "information sharing "effect.